In the course of implementing #11, I made various changes to the
monorepo that I deemed either necessary or simply beneficial. Here these
changes are extracted from #11, which has been separated into this PR
and #16. Contains the following changes:

- Upgrade `ts-bridge` and migrate all packages to ESM
- In the course of implementing #11, I ran into a [TypeScript project
references](https://www.typescriptlang.org/docs/handbook/project-references.html)-related
error, because [`ts-bridge`](https://ts-bridge.dev/) originally did not
support this feature. However, [`ts-bridge` recently added support for
project
references](https://github.com/ts-bridge/ts-bridge/releases/tag/v7.0.0),
and updating fixed the problem.
- This, however, necessitated migrating all monorepo packages to be
ESM-first (`"type": "module"`), and setting TypeScript's
`moduleResolution` algorithm to `Node16`. So, now the entire monorepo is
ESM-first, but any libraries we publish will still be importable in
CommonJS, due to `ts-bridge`.
- As part of this change, `.js` files were renamed to `.cjs`, and `.mjs`
files to `.js`. The same goes for their `.ts` equivalents.
- A notable exception includes the published files in `@ocap/shims`,
which retain their `.mjs` extensions as a redundancy measure.
- Fix intra-repo path resolution in tests
- In the `/snaps` and `/core` monorepos, Jest's `moduleNameMapper`
option is manually configured to match the `paths` property in
`tsconfig.json` to ensure that tests use source code as opposed to build
outputs.
- In `vite`, we accomplish the same by dropping in the plugin
`vite-tsconfig-paths`, with no additional configuration whatsoever.
- Add internal `test-utils` package
- Rather than keeping a folder of test utilities at the monorepo root, I
decided to just create an internal package for this purpose.
- Set the version of all intra-monorepo dependencies to `workspace:^`
- This takes a queue from the Snaps monorepo. In this way, we will never
accidentally pull a workspace package from npm.
- Note that this required stealing some of the Snaps monorepo's
constraints for our `constraints.pro`. However, don't spend too much
time on that file, because it will be replaced soon: #17
- Externalize `endoify.mjs` in `extension` HTML files
- Introduces our own tiny `vite` plugin, `endoifyHtmlFilesPlugin`, that
inserts the `endoify.mjs` in the correct place just before HTML files
are built. `vite`'s aggressive optimization and module resolution logic
otherwise prevents us from doing this.
- Add `clean` script to all packages
- After experiencing some issues with cached builds, I decided to make
sure every package has a `clean` script.

This bumps `typescript@5.5.4` once again, reapplying changes from #23
which were accidentally reverted in #16.

This also applies minor patches to `packages/shims/scripts/bundle.js` to
prevent a known failure in `node@18`.